The present invention relates to spread-spectrum communications and more particularly to a method and apparatus for enhancing communications by using phased array principles for increasing signal-to-noise ratio for a spread spectrum signal with multipath arriving at a receiver.
Achieving sufficient signal strength when a received signal comes from two paths is a problem when communicating with spread-spectrum modulation in a multipath environment. The received signal from the two paths may have phase cancellation, yielding no reception, or reception with an unacceptable error rate.
Phased arrays, as is well known in the art, require N antenna elements for distinguishing up to N-1 signals arriving at the phased array from different paths or directions. This concept of spatial diversity is well developed in antenna theory.
A spread spectrum phased array receiver has a set of phased array antennas. The set of phased array antennas receive a spread spectrum signal containing a plurality of channels. The receiver outputs timed versions of the received signal. Each timed version is associated with a respective one out of the set of phased array antennas. A plurality of despread signals is produced by despreading each timed version of the received signal using a plurality of chip code sequences associated with the channels. The despread signals are combined as a despread signal. A magnitude of the combined despread signal is determined for obtaining a present and a prior magnitude. The present and prior magnitude are compared. A delay associated with the timed versions is adjusted in response to the comparison so antenna beams are steered towards components of the spread spectrum signal with a highest combined magnitude.